Actually, Pretani is geographical as well. The Preta part of the name is related to Creta, as in chalk and the Cretaceous period in which it was laid down. The word was in Celtic languages, one in the P Celtic, the other in the Q Celtic form. So the Pretani live on the chalk land aka Prydain, Albion (white?) etc. Since Ireland has chalk, it's not too inappropriate as a geographical description.

Penny